1. Field of the Invention
This invention relates generally to sheet feeding in copier/printers, and more particularly, to a system for checking for changes in sheet sizes in the paper trays of such machines.
2. Description of Related Art
In a typical electrophotographic printing process, a photoconductive member is charged to a substantially uniform potential so as to sensitize the surface thereof. The charged portion of the photoconductive member is exposed to a light image of an original document being reproduced. Exposure of the charged photoconductive member selectively dissipates the charges thereon in the irradiated areas. This records an electrostatic latent image on the phototconductive member corresponding to the informational areas contained within the original document. After the electrostatic latent image is recorded on the phototconductive member, the latent image is developed by bringing a developer material into contact therewith. Generally, the developer material comprises toner particles adhering triboelectrically to carrier granules to the latent image forming a toner powder image on the photoconductive member. The toner powder image is then transferred from the photoconductive member to a copy sheet. The toner particles are heated to permanently affix the powder image to the copy sheet.
One problem encountered with printers and copiers is unscheduled maintenance calls which can be very costly, and especially, if the unscheduled maintenance calls are initiated by wrong substrate size settings by customers.
After a machine feeds a sheet from a tray, the sheet""s travel inside the machine is monitored with paper path sensors that have to be cleared at predetermined times. The time from the sheet""s leading edge making a sensor to the trail edge clearing the sensor is nominally the sheet length divided by the transport speed. Obviously, this time is different for different sheet lengths. Machines use predetermined timer values for different sheet lengths and should the sheet length be incorrectly set-up, the result is timing error and machine shutdown. Also, should the sheet""s actual width be different from the set-up, the machine will print images, undesirably, to the wrong places.
If the size setting for a tray is incorrect, the machine will shutdown continuously at each feed from the tray and if the customer cannot identify the problem to be a simple, (and possibly self-inflected) set-up mismatch, a maintenance engineer may be called. This could happen when the customer has a full service contract that does not add to the customer""s direct costs, but the cost is fully realized by the maintenance engineer""s employer.
A number of attempts have been made to ensure the correct sheet size settings in machines. For example, customers are encouraged to set up the sizes through the user interface; or set up the sizes with a special indicator in the trays that is read with sensors; or machines are equipped with automatic size sensing systems where the machine has sensors to detect the positions of substrate guides in a tray and from this deduce the size of substrates in the tray.
U.S. Pat. No. 4,475,732 issued Oct. 9, 1984 to Clausing et al. discloses in FIG. 3 the use of a stack height sensor in a sheet feeding and separating apparatus with the sensor incorporating a plunger having a flag attached to a shoulder thereof that blocks and unblocks an optoelectric sensor as the plunger is moved in a vertical direction.
While the above-mentioned attempts to ensure the correct sheet size settings in machines have been useful, there is still a need for low cost improvements.
Accordingly, pursuant to the features of the present invention, an improved system to detect if the positions of a tray""s sheet guides have been changed while the tray has been open is disclosed that answers the above-mentioned problem by providing a spring loaded stud in the tray that is pushed and locked into an xe2x80x98inxe2x80x99 position every time the tray is pushed in. When the tray is pulled out, if the size guides are moved, the spring-loaded stud is released with a linkage mechanism from the guides to the stud. The stud actuates a sensor flag, and as the tray is pushed home, a sensor checks the flag and a control system subsequently deduces whether the guides have been moved.
These and other features and advantages of the invention are described in or apparent from the following detailed description of the exemplary embodiments.